fix: make the CLI usable without the bigquery extra

[anaselmhamdi]

pip install bizon with no extras produces a CLI that cannot start at all. Every command — bizon --help included — dies with:

ImportError: cannot import name 'bigquery' from 'google.cloud'

Pre-existing, not from #84. v0.4.1 fails identically in a clean venv; I found it while smoke-testing the v0.5.0 artifact from PyPI. It has presumably gone unnoticed because nearly everyone installs an extra — but it makes the advertised base package unusable, including for anyone who only wants the file or logger destination.

Cause

bizon.common.models imports every destination config unconditionally (pydantic needs the classes to build the discriminated union). The BigQuery config imports table_naming purely for the BIZON_TABLE_PREFIX string constant, and table_naming imported google at module level — so the entire CLI transitively depended on the bigquery extra.

I checked the rest of that chain: table_naming was the only heavy module-level import across all five destination config modules. The other two BigQuery configs reach it the same way, for the same constant.

Fix

Import google inside resolve_default_table_id() — the only thing that needs it, and only reached when a BigQuery destination is actually writing. The type annotation moves behind TYPE_CHECKING with from __future__ import annotations.

Verified

• Installed this tree with no extras into a fresh venv (confirming google.cloud.bigquery genuinely absent): bizon --help and bizon source list work, and a dummy → file pipeline runs to completion — 5 rows written.
• import bizon.cli.main now pulls in zero optional dependencies.
• Full suite: 285 passed, nothing failing outside the pre-existing GCP-credential set.

Regression test

tests/cli/test_cli_imports.py asserts on sys.modules in a subprocess rather than catching an ImportError, so it fails in a dev environment where every extra is installed — otherwise it would be vacuous in CI. I confirmed it fails on the pre-fix code:

AssertionError: Importing bizon.cli.main pulled in optional dependencies:
['google.cloud.bigquery']. Every CLI command will fail on an install
without the matching extra. Import these lazily, inside the function that needs them.

Worth a 0.5.1 once merged, since 0.5.0 ships the bug.

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